Heuristic safety net for transitioning configurations in a neural stimulation system

ABSTRACT

A system and method using a plurality of electrodes. An immediate virtual multipole is defined, an immediate electrode configuration emulating the immediate virtual multipole is defined, electrical energy is conveyed to the electrodes in accordance with the immediate electrode configuration, a new virtual multipole is defined by changing a parameter of the immediate virtual multipole by a step size, a new electrode configuration that emulates the new virtual multipole is defined, a difference value as a function of the immediate virtual multipole and the new virtual multipole is computed, the different value is compared to a limit value, electrical energy is conveyed to the electrodes in accordance with the new electrode configuration if the difference value does not exceed the limit value, and the absolute value of the step size is decreased to create a new step size if the difference value does exceed the limit value.

RELATED APPLICATION DATA

The present application is a continuation of U.S. patent applicationSer. No. 13/849,375, filed Mar. 22, 2013, which claims the benefit under35 U.S.C. §119 to U.S. Provisional Patent Application Ser. No.61/614,853, filed Mar. 23, 2012. The foregoing applications are eachhereby incorporated by reference into the present application in theirentirety.

FIELD OF THE INVENTION

The present disclosure relates to tissue stimulation systems, and moreparticularly, to neurostimulation systems for programmingneurostimulation leads.

BACKGROUND OF THE INVENTION

Implantable neurostimulation systems have proven therapeutic in a widevariety of diseases and disorders. Pacemakers and Implantable CardiacDefibrillators (ICDs) have proven highly effective in the treatment of anumber of cardiac conditions (e.g., arrhythmias). Spinal CordStimulation (SCS) systems have long been accepted as a therapeuticmodality for the treatment of chronic pain syndromes, and theapplication of tissue stimulation has begun to expand to additionalapplications such as angina pectoralis and incontinence. Deep BrainStimulation (DBS) has also been applied therapeutically for well over adecade for the treatment of refractory chronic pain syndromes, and DBShas recently been applied in additional areas such as movement disordersand epilepsy. Further, in recent investigations, Peripheral NerveStimulation (PNS) systems have demonstrated efficacy in the treatment ofchronic pain syndromes and incontinence, and a number of additionalapplications are currently under investigation. Furthermore, FunctionalElectrical Stimulation (FES) systems, such as the Freehand system byNeuroControl (Cleveland, Ohio), have been applied to restore somefunctionality to paralyzed extremities in spinal cord injury patients.

These implantable neurostimulation systems typically include one or moreelectrode carrying stimulation leads, which are implanted at the desiredstimulation site, and a neurostimulator (e.g., an implantable pulsegenerator (IPG)) implanted remotely from the stimulation site, butcoupled either directly to the neurostimulation lead(s) or indirectly tothe neurostimulation lead(s) via a lead extension. The neurostimulationsystem may further comprise an external control device to remotelyinstruct the neurostimulator to generate electrical stimulation pulsesin accordance with selected stimulation parameters.

Electrical stimulation energy may be delivered from the neurostimulatorto the electrodes in the form of an electrical pulsed waveform. Thus,stimulation energy may be controllably delivered to the electrodes tostimulate neural tissue. The configuration of electrodes used to deliverelectrical pulses to the targeted tissue constitutes an electrodeconfiguration, with the electrodes capable of being selectivelyprogrammed to act as anodes (positive), cathodes (negative), or left off(zero). In other words, an electrode configuration represents thepolarity being positive, negative, or zero. Other parameters that may becontrolled or varied include the amplitude, width, and rate of theelectrical pulses provided through the electrode array. Each electrodeconfiguration, along with the electrical pulse parameters, can bereferred to as a “stimulation parameter set.”

With some neurostimulation systems, and in particular, those withindependently controlled current or voltage sources, the distribution ofthe current to the electrodes (including the case of theneurostimulator, which may act as an electrode) may be varied such thatthe current is supplied via numerous different electrode configurations.In different configurations, the electrodes may provide current orvoltage in different relative percentages of positive and negativecurrent or voltage to create different electrical current distributions(i.e., fractionalized electrode configurations).

As briefly discussed above, an external control device can be used toinstruct the neurostimulator to generate electrical stimulation pulsesin accordance with the selected stimulation parameters. Typically, thestimulation parameters programmed into the neurostimulator can beadjusted by manipulating controls on the external control device tomodify the electrical stimulation provided by the neurostimulator systemto the patient. Thus, in accordance with the stimulation parametersprogrammed by the external control device, electrical pulses can bedelivered from the neurostimulator to the stimulation electrode(s) tostimulate or activate a volume of tissue in accordance with a set ofstimulation parameters and provide the desired efficacious therapy tothe patient. The best stimulus parameter set will typically be one thatdelivers stimulation energy to the volume of tissue that must bestimulated in order to provide the therapeutic benefit (e.g., treatmentof pain), while minimizing the volume of non-target tissue that isstimulated.

However, the number of electrodes available combined with the ability togenerate a variety of complex stimulation pulses, presents a hugeselection of stimulation parameter sets to the clinician or patient. Forexample, if the neurostimulation system to be programmed has an array ofsixteen electrodes, millions of stimulation parameter sets may beavailable for programming into the neurostimulation system. Today,neurostimulation system may have up to thirty-two electrodes, therebyexponentially increasing the number of stimulation parameters setsavailable for programming.

To facilitate such selection, the clinician generally programs theneurostimulator through a computerized programming system. Thisprogramming system can be a self-contained hardware/software system, orcan be defined predominantly by software running on a standard personalcomputer (PC). The PC or custom hardware may actively control thecharacteristics of the electrical stimulation generated by theneurostimulator to allow the optimum stimulation parameters to bedetermined based on patient feedback or other means, and subsequently toprogram the neurostimulator with the optimum stimulation parameter setor sets. The computerized programming system may be operated by aclinician attending the patient in several scenarios.

For example, in order to achieve an effective result from SCS, the leador leads must be placed in a location, such that the electricalstimulation will cause paresthesia. The paresthesia induced by thestimulation and perceived by the patient should be located inapproximately the same place in the patient's body as the pain that isthe target of treatment. If a lead is not correctly positioned, it ispossible that the patient will receive little or no benefit from animplanted SCS system. Thus, correct lead placement can mean thedifference between effective and ineffective pain therapy. Whenelectrical leads are implanted within the patient, the computerizedprogramming system, in the context of an operating room (OR) mappingprocedure, may be used to instruct the neurostimulator to applyelectrical stimulation to test placement of the leads and/or electrodes,thereby assuring that the leads and/or electrodes are implanted ineffective locations within the patient.

Once the leads are correctly positioned, a fitting procedure, which maybe referred to as a navigation session, may be performed using thecomputerized programming system to program the external control device,and if applicable the neurostimulator, with a set of stimulationparameters that best addresses the painful site. Thus, the navigationsession may be used to pinpoint the volume of activation (VOA) or areascorrelating to the pain. Such programming ability is particularlyadvantageous for targeting the tissue during implantation, or afterimplantation should the leads gradually or unexpectedly move that wouldotherwise relocate the stimulation energy away from the target site. Byreprogramming the neurostimulator (typically by independently varyingthe stimulation energy on the electrodes), the volume of activation(VOA) can often be moved back to the effective pain site without havingto re-operate on the patient in order to reposition the lead and itselectrode array. When adjusting the volume of activation (VOA) relativeto the tissue, it is desirable to make small changes in the proportionsof current, so that changes in the spatial recruitment of nerve fiberswill be perceived by the patient as being smooth and continuous and tohave incremental targeting capability.

One known computerized programming system for SCS is called the BionicNavigator®, available from Boston Scientific NeuromodulationCorporation. The Bionic Navigator® is a software package that operateson a suitable PC and allows clinicians to program stimulation parametersinto an external handheld programmer (referred to as a remote control).Each set of stimulation parameters, including fractionalized currentdistribution to the electrodes (as percentage cathodic current,percentage anodic current, or off), may be stored in both the BionicNavigator® and the remote control and combined into a stimulationprogram that can then be used to stimulate multiple regions within thepatient.

To determine the stimulation parameters to be programmed, the BionicNavigator® may be operated by a clinician in one of three modes: (a) amanual programming mode to manually select the cathodic current andanodic current flowing through the electrodes; (b) an electronictrolling (“e-troll”) mode to quickly sweep the electrode array using alimited number of electrode configurations to gradually move a cathodein bipolar stimulation; and (c) a Navigation programming mode to finetune and optimize stimulation coverage for patient comfort using a widenumber of electrode configurations. These three modes allow theclinician to determine the most efficient stimulation parameter sets fora given patient.

In the manual programming mode, the clinician directly selectsindividual electrodes and the current magnitude and polarity to beapplied to each selected electrode. In the navigation and e-trollprogramming modes, the Bionic Navigator® semi-automatically transitionsbetween different electrode configurations to electrically “steer” thecurrent along the implanted leads in real-time (e.g., using a joystickor joystick-like controls) in a systematic manner, thereby allowing theclinician to determine the most efficacious stimulation parameter setsthat can then be stored and eventually combined into stimulationprograms. In the context of SCS, current steering is typically eitherperformed in a rostro-caudal direction (i.e., along the axis of thespinal cord) or a medial-lateral direction (i.e., perpendicular to theaxis of the spinal cord).

The navigation and e-troll programming modes differ in part in the wayin which the clinician changes electrode configurations from oneconfiguration to another. E-troll programming mode utilizes a techniqueknown as “panning,” which shifts a pre-defined electrode configurationdown the sequence of electrodes without changing the basic form of theelectrode configuration. Navigation programming mode utilizes atechnique known as “weaving,” which moves the anode or anodes around thecathode, while slowly progressing the cathode down the sequence ofelectrodes. The e-troll and Navigation programming modes may havedifferent clinical uses (e.g., finding the “sweet spot” in the case ofpanning, or shaping the electrical field around the cathode in the caseof weaving).

In one novel current steering method, described in U.S. patentapplication Ser. No. 12/938,282, entitled “System and Method for MappingArbitrary Electric Fields to Pre-existing Lead Electrodes,” which isexpressly incorporated herein by reference, a stimulation target in theform of a virtual pole (e.g., a virtual bipole or tripole) is definedand the stimulation parameters, including the fractionalized currentvalues on each of the electrodes, are computationally determined in amanner that emulates these virtual poles. It can be appreciated thatcurrent steering can be implemented by moving the virtual poles aboutthe leads, such that the appropriate fractionalized current values forthe electrodes are computed for each of the various positions of thevirtual pole. As a result, the current steering can be implemented usingan arbitrary number and arrangement of electrodes, thereby solving theafore-described problems.

When performing current steering, it is desirable that the transitionsin the resulting electrical field be as smooth as possible, such thatthe patient does not experience drastic changes in the stimulationregimen, which may either result in an uncomfortable or even painfulsensation caused by overstimulation or a sudden loss of therapy causedby understimulation. In the context of SCS, cathodic electrodes dominatethe stimulation effect, and thus, the overstimulation may occur whenthere is a significant increase in the percentage of current on certaincathodic electrodes, and understimulation may occur when there is asignificant decrease of the percentage of current on certain cathodicelectrodes. There, thus, remains a need to ensure that the transitionsbetween electrode configurations be as smooth as possible during currentsteering.

SUMMARY OF THE INVENTION

In accordance with the present inventions, a system for an electricalneurostimulator coupled to a plurality of electrodes and a method ofoperating the same to provide therapy to a patient is provided. Thesystem comprises telemetry circuitry configured for communicating withthe electrical neurostimulator, and a controller/processor. The systemmay further comprises a user interface configured for receiving a userinput. The system may also comprise a housing containing the telemetrycircuitry and the controller/processor. This system and method mayimplement one or more of several techniques for smoothly transitioningelectrical stimulation energy between different electrodeconfigurations.

One technique comprises (a) defining an immediate virtual multipole, (b)defining an immediate electrode configuration (e.g., a fractionalizedcombination) that emulates the immediate virtual multipole, (c)instructing the electrical neurostimulator via the telemetry circuitryto convey electrical energy to the plurality of electrodes in accordancewith the immediate electrode configuration, (d) defining a new virtualmultipole by changing a parameter (e.g., a location, focus, and/or upperanode percentage) of the immediate virtual multipole by a step size(which may be either positive or negative), and (e) defining a newelectrode configuration (e.g., a fractionalized combination) thatemulates the new virtual multipole.

This technique further comprises (f) computing a difference value as afunction of the immediate virtual multipole and the new virtualmultipole. In one embodiment, the difference value is a function of theimmediate electrode configuration and the new electrode configuration.For example, the difference value may comprise a change in a cathodiccurrent on an individual one of the electrodes, a change in an anodiccurrent on an individual one of the electrodes, a total change incathodic current on the electrodes, or a total change in anodic currenton the electrodes. In another embodiment, the difference value is afunction of one of an electrical field, absolute potential, currentdensity, an activating function, and a total net driving function thatis derived from the immediate virtual multipole and the new virtualmultipole. In still another embodiment, the difference value is adisplacement between one pole of the immediate virtual multipole and acorresponding pole of the new virtual multipole.

This technique further comprises (g) comparing the difference value to alimit value, (h) instructing the electrical neurostimulator to conveyelectrical energy to the plurality of electrodes in accordance with thenew electrode configuration if the difference value does not exceed thelimit value; and (i) not instructing the electrical neurostimulator toconvey electrical energy to the plurality of electrodes, decreasing theabsolute value of the step size to create a new step size, and repeatingsteps (d)-(i) for the new step size if the difference value exceeds thelimit value.

In one embodiment, this technique comprises (d) defining the new virtualmultipole by changing another parameter of the immediate virtualmultipole by another step size, and (i) decreasing the absolute value ofthe other step size to create another new step size, and repeating steps(d)-(i) for the new step size and the other new step size if thedifference value exceeds the limit value. In another embodiment, thetechnique comprises (f) computing another difference value as anotherfunction of the immediate virtual multipole and the new virtualmultipole, (g) comparing the other difference value to another limitvalue, (h) instructing the electrical neurostimulator to convey theelectrical energy to the plurality of electrodes in accordance with thenew set of stimulation parameters if neither the difference valueexceeds the limit value nor the other difference value exceeds the otherlimit value, and (i) decreasing the absolute value of the step size tocreate the new step size and repeating steps (d)-(i) for the new stepsize if either the difference value exceeds the limit value or the otherdifference value exceeds the other limit value.

Another technique comprises defining an immediate electrodeconfiguration, conveying electrical energy to the plurality ofelectrodes in accordance with the immediate electrode configuration,defining a final electrode configuration, defining a series ofintermediate electrode configurations using a heuristic set of rulesbased on the immediate electrode configuration and the final electrodeconfiguration, instructing the electrical neurostimulator to conveyelectrical energy to the plurality of electrodes in accordance with theseries of intermediate electrode configurations, and instructing theelectrical neurostimulator to convey electrical energy to the pluralityof electrodes in accordance with the subsequent electrode configuration.

The series of intermediate electrode configurations may be defined byrepeatedly defining a next intermediate electrode configuration based onan immediate previously defined electrode configuration and the finalelectrode configuration until the next intermediate electrodeconfiguration matches the final electrode configuration. In this case,the heuristic set of rules may comprise limiting shifting of the anodicand/or cathodic current from the immediate previously defined electrodeconfiguration to the next intermediate electrode configuration based onone or more of the following: a maximum change in a cathodic current onan individual one of the electrodes, a maximum change in an anodiccurrent on an individual one of the electrodes, a total maximum changein cathodic current on the electrodes, and a total maximum change inanodic current on the electrodes.

In one embodiment, each of the electrodes has an electrical currenttransition between the immediate previously defined electrodeconfiguration and the final electrode configuration that is one of thefollowing: no current change transition, a cathodic current increasetransition, a cathodic current decrease transition, a cathodic currentdecrease/anodic current increase transition, an anodic current increasetransition, an anodic current decrease transition, and an anodic currentdecrease/cathodic current increase transition, and wherein thecontroller/processor is configured for applying the heuristic set ofrules to the electrical current transitions to define the nextintermediate electrode configuration.

The shift in the electrical current will depend on the transitionbetween the immediate previously defined electrode configuration and thefinal electrode configuration.

For example, if one of the electrodes has a cathodic decreasetransition, and another one of the electrodes has a cathodic increasetransition, the heuristic set of rules may shift the cathodic currentfrom the one electrode to the other one electrode.

As another example, if one of the electrodes has an anodic currentdecrease/cathodic current increase transition, the heuristic set ofrules may shift the anodic current from the one electrode to another oneof the electrodes, which may, e.g., have an anodic current increasetransition, or may have no current change transition or an anodiccurrent decrease transition. At least one more of the electrodes mayhave an anodic current decrease/cathodic current increase transition,and the one electrode may have a greater cathodic current than does theat least one more electrode for the final electrode configuration.

As still another example, if one of the electrodes has a cathodiccurrent decrease/anodic current increase transition, the heuristic setof rules may comprise shifting cathodic current from the one electrodeto another one of the electrodes, which may, e.g., have a cathodiccurrent increase transition, or may have no current change transition ora cathodic current decrease transition. The other one electrode may havea cathodic current decrease/anodic current increase transition, and theother one electrode may have the greatest cathodic current for the finalelectrode configuration.

As yet another example, if one of the electrodes has an anodic decreasetransition, and another one of the electrodes has an anodic increasetransition, the heuristic set of rules may shift the anodic current fromthe one electrode to the other one electrode.

The heuristic rules can be combined into a series of inquiries thatprioritizes the electrodes for which the electrical current will beshifted.

For example, the heuristic set of rules may comprise determining whetherthere exists a first electrode pairing having a cathodic currentincrease transition and a cathodic current decrease transition, andshifting cathodic current from the electrode having the cathodic currentdecrease transition to the electrode having the cathodic currentincrease transition if the first electrode pairing is determined toexist; determining whether there exists a second electrode pairinghaving a cathodic current increase transition and a cathodic currentdecrease/anodic current increase transition, and shifting cathodiccurrent from the electrode having the cathodic current decrease/anodiccurrent increase transition to the electrode having the cathodic currentincrease transition if the second electrode pairing is determined toexist; determining whether there exists a third electrode pairing havingan anodic current increase transition and an anodic current decreasetransition, and shifting anodic current from the electrode having theanodic current decrease transition to the electrode having the anodiccurrent increase transition if the third electrode pairing is determinedto exist; and determining whether there exists a fourth electrodepairing having an anodic current increase transition and an anodiccurrent decrease/cathodic current increase transition, and shiftinganodic current from the electrode having the anodic currentdecrease/cathodic current increase transition to the electrode havingthe anodic current increase transition if the fourth electrode pairingis determined to exist.

If none of the first, second, third, and fourth electrode pairingsexists, the heuristic set of rules may comprise determining whetherthere exists a first electrode having an anodic currentdecrease/cathodic current increase transition and whether there exists asecond electrode having either a no current change transition or ananodic current decrease transition. If the first and second electrodeexists, the heuristic set of rules shifts anodic current from the firstelectrode to the second electrode. If either the first electrode or thesecond electrode does not exist, the heuristic set of rules comprisesshifting cathodic current from an electrode having a cathodic currentdecrease/anodic current increase transition to an electrode havingeither a no current change transition or a cathodic current decreasetransition.

The heuristic set of rules may further comprise determining whether allof the electrodes either have a cathodic current decrease/anodic currentincrease transition or an anodic current decrease/cathodic currentdecrease transition. If all of the electrodes either have a cathodiccurrent decrease/anodic current increase transition or an anodic currentdecrease/cathodic current decrease transition, the heuristic set ofrules further comprises determining whether there exists multipleelectrodes each having an anodic current decrease/cathodic currentincrease transition, and if the multiple electrodes exist, determiningwhich one of the multiple electrodes has the greatest cathodic currentfor the final electrode configuration, and shifting anodic current fromthe one electrode to another electrode. The heuristic set of rulesfurther comprises, if the multiple electrodes do not exist, determiningone electrode having the greatest cathodic current for the previousintermediate electrode configuration, and shifting cathodic current fromany electrode having cathodic current for the previous intermediateelectrode configuration to the one electrode.

Other and further aspects and features of the disclosure will be evidentfrom reading the following detailed description of the preferredembodiments, which are intended to illustrate, not limit, thedisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of preferred embodimentsof the present disclosure, in which similar elements are referred to bycommon reference numerals. In order to better appreciate how theabove-recited and other advantages and objects of the present disclosureare obtained, a more particular description of the present disclosurebriefly described above will be rendered by reference to specificembodiments thereof, which are illustrated in the accompanying drawings.Understanding that these drawings depict only typical embodiments of thedisclosure and are not therefore to be considered limiting of its scope,the disclosure will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1 is a plan view of a Spinal cord Stimulation (SCS) systemconstructed in accordance with one embodiment of the present disclosure;

FIG. 2 is a perspective view of the arrangement of the SCS system ofFIG. 1 with respect to a patient;

FIG. 3 is a profile view of an implantable pulse generator (IPG) andpercutaneous leads used in the SCS system of FIG. 1;

FIG. 4 is front view of a remote control (RC) used in the SCS system ofFIG. 1;

FIG. 5 is a block diagram of the internal components of the RC of FIG.4;

FIG. 6 is a block diagram of the internal components of a clinician'sprogrammer (CP) used in the SCS system of FIG. 1;

FIG. 7 is a plan view of a user interface of the CP of FIG. 6 forprogramming the IPG of FIG. 3 in a manual mode;

FIG. 8 is a plan view of a user interface of the CP of FIG. 6 forprogramming the IPG of FIG. 3 in an e-troll mode;

FIG. 9 is a panned sequence of a multipole used by the e-troll mode ofFIG. 8 to program the IPG of FIG. 3;

FIG. 10 is a plan view of the user interface of FIG. 8, particularlyshowing the expansion of the Advanced Tab into resolution and focuscontrols;

FIG. 11 is a plan view of a user interface of the CP of FIG. 6 forprogramming the IPG of FIG. 3 in a Navigation mode;

FIG. 12 is a sequence of different virtual multipoles used by theNavigation mode of FIG. 10 to program the IPG of FIG. 3;

FIG. 13 is a plot illustrating a weaving space for the sequence of themultipoles illustrated in FIG. 12;

FIG. 14 is a flow chart illustrating one method used by the SCS systemof FIG. 1 to steer electrical current in accordance with one set ofheuristic rules;

FIGS. 15A and 15B are flows charts illustrating another method used bythe SCS system of FIG. 1 to steer electrical current in accordance withanother set of heuristic rules;

FIG. 16 is a schematic illustrating the intermediate current transitionsperformed by the heuristic rules illustrated in FIG. 15B to transitionbetween one exemplary set of initial and final electrode configurations;

FIG. 17 (17-1-17-2) is a schematic illustrating the intermediate currenttransitions performed by the heuristic rules illustrated in FIG. 15B totransition between another exemplary set of initial and final electrodeconfigurations;

FIG. 18 (18-1-18-2) is a schematic illustrating the intermediate currenttransitions performed by the heuristic rules illustrated in FIG. 15B totransition between still another exemplary set of initial and finalelectrode configurations; and

FIG. 19 (19-1-19-2) is a schematic illustrating the intermediate currenttransitions performed by the heuristic rules illustrated in FIG. 15B totransition between yet another exemplary set of initial and finalelectrode configurations.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The description that follows relates to spinal cord stimulation (SCS)system. However, it is to be understood that the while the inventionlends itself well to applications in SCS, the invention, in its broadestaspects, may not be so limited. Rather, the invention may be used withany type of implantable electrical circuitry used to stimulate tissue.For example, the present invention may be used as part of a pacemaker, adefibrillator, a cochlear stimulator, a retinal stimulator, a stimulatorconfigured to produce coordinated limb movement, a cortical stimulator,a deep brain stimulator, peripheral nerve stimulator, microstimulator,or in any other neural stimulator configured to treat urinaryincontinence, sleep apnea, shoulder sublaxation, headache, etc.

Turning first to FIG. 1, an exemplary SCS system 10 generally includes aplurality (in this case, two) of implantable neurostimulation leads 12,an implantable pulse generator (IPG) 14, an external remote controllerRC 16, a clinician's programmer (CP) 18, an external trial stimulator(ETS) 20, and an external charger 22.

The IPG 14 is physically connected via one or more percutaneous leadextensions 24 to the neurostimulation leads 12, which carry a pluralityof electrodes 26 arranged in an array. In the illustrated embodiment,the neurostimulation leads 12 are percutaneous leads, and to this end,the electrodes 26 are arranged in-line along the neurostimulation leads12. The number of neurostimulation leads 12 illustrated is two, althoughany suitable number of neurostimulation leads 12 can be provided,including only one. Alternatively, a surgical paddle lead in can be usedin place of one or more of the percutaneous leads. As will be describedin further detail below, the IPG 14 includes pulse generation circuitrythat delivers electrical stimulation energy in the form of a pulsedelectrical waveform (i.e., a temporal series of electrical pulses) tothe electrode array 26 in accordance with a set of stimulationparameters.

The ETS 20 may also be physically connected via the percutaneous leadextensions 28 and external cable 30 to the neurostimulation leads 12.The ETS 20, which has similar pulse generation circuitry as the IPG 14,also delivers electrical stimulation energy in the form of a pulseelectrical waveform to the electrode array 26 accordance with a set ofstimulation parameters. The major difference between the ETS 20 and theIPG 14 is that the ETS 20 is a non-implantable device that is used on atrial basis after the neurostimulation leads 12 have been implanted andprior to implantation of the IPG 14, to test the responsiveness of thestimulation that is to be provided. Thus, any functions described hereinwith respect to the IPG 14 can likewise be performed with respect to theETS 20. Further details of an exemplary ETS are described in U.S. Pat.No. 6,895,280, which is expressly incorporated herein by reference.

The RC 16 may be used to telemetrically control the ETS 20 via abi-directional RF communications link 32. Once the IPG 14 andneurostimulation leads 12 are implanted, the RC 16 may be used totelemetrically control the IPG 14 via a bi-directional RF communicationslink 34. Such control allows the IPG 14 to be turned on or off and to beprogrammed with different stimulation parameter sets. The IPG 14 mayalso be operated to modify the programmed stimulation parameters toactively control the characteristics of the electrical stimulationenergy output by the IPG 14. As will be described in further detailbelow, the CP 18 provides clinician detailed stimulation parameters forprogramming the IPG 14 and ETS 20 in the operating room and in follow-upsessions.

The CP 18 may perform this function by indirectly communicating with theIPG 14 or ETS 20, through the RC 16, via an IR communications link 36.Alternatively, the CP 18 may directly communicate with the IPG 14 or ETS20 via an RF communications link (not shown). The clinician detailedstimulation parameters provided by the CP 18 are also used to programthe RC 16, so that the stimulation parameters can be subsequentlymodified by operation of the RC 16 in a stand-alone mode (i.e., withoutthe assistance of the CP 18).

The external charger 22 is a portable device used to transcutaneouslycharge the IPG 14 via an inductive link 38. For purposes of brevity, thedetails of the external charger 22 will not be described herein. Detailsof exemplary embodiments of external chargers are disclosed in U.S. Pat.No. 6,895,280, which has been previously incorporated herein byreference. Once the IPG 14 has been programmed, and its power source hasbeen charged by the external charger 22 or otherwise replenished, theIPG 14 may function as programmed without the RC 16 or CP 18 beingpresent.

As shown in FIG. 2, the neurostimulation leads 12 are implanted withinthe spinal column 42 of a patient 40. The preferred placement of theneurostimulation leads 12 is adjacent, i.e., resting upon, the spinalcord area to be stimulated. Due to the lack of space near the locationwhere the neurostimulation leads 12 exit the spinal column 42, the IPG14 is generally implanted in a surgically-made pocket either in theabdomen or above the buttocks. The IPG 14 may, of course, also beimplanted in other locations of the patient's body. The lead extension24 facilitates locating the IPG 14 away from the exit point of theneurostimulation leads 12. As there shown, the CP 18 communicates withthe IPG 14 via the RC 16.

Referring now to FIG. 3, the external features of the neurostimulationleads 12 and the IPG 14 will be briefly described. One of theneurostimulation leads 12 a has eight electrodes 26 (labeled E1-E8), andthe other stimulation lead 12 b has eight electrodes 26 (labeledE9-E16). The actual number and shape of leads and electrodes will, ofcourse, vary according to the intended application. The IPG 14 comprisesan outer case 44 for housing the electronic and other components(described in further detail below), and a connector 46 to which theproximal ends of the neurostimulation leads 12 mates in a manner thatelectrically couples the electrodes 26 to the electronics within theouter case 44. The outer case 44 is composed of an electricallyconductive, biocompatible material, such as titanium, and forms ahermetically sealed compartment wherein the internal electronics areprotected from the body tissue and fluids. In some cases, the outer case44 may serve as an electrode.

The IPG 14 includes a battery and pulse generation circuitry thatdelivers the electrical stimulation energy in the form of a pulsedelectrical waveform to the electrode array 26 in accordance with a setof stimulation parameters programmed into the IPG 14. Such stimulationparameters may comprise electrode configurations, which define theelectrodes that are activated as anodes (positive), cathodes (negative),and turned off (zero), percentage of stimulation energy assigned to eachelectrode (fractionalized electrode configurations), and electricalpulse parameters, which define the pulse amplitude (measured inmilliamps or volts depending on whether the IPG 14 supplies constantcurrent or constant voltage to the electrode array 26), pulse width(measured in microseconds), and pulse rate (measured in pulses persecond).

Electrical stimulation will occur between two (or more) activatedelectrodes, one of which may be the IPG case. Simulation energy may betransmitted to the tissue in a monopolar or multipolar (e.g., bipolar,tripolar, etc.) fashion. Monopolar stimulation occurs when a selectedone of the lead electrodes 26 is activated along with the case of theIPG 14, so that stimulation energy is transmitted between the selectedelectrode 26 and case. Bipolar stimulation occurs when two of the leadelectrodes 26 are activated as anode and cathode, so that stimulationenergy is transmitted between the selected electrodes 26. For example,electrode E3 on the first lead 12 may be activated as an anode at thesame time that electrode E11 on the second lead 12 is activated as acathode. Tripolar stimulation occurs when three of the lead electrodes26 are activated, two as anodes and the remaining one as a cathode, ortwo as cathodes and the remaining one as an anode. For example,electrodes E4 and E5 on the first lead 12 may be activated as anodes atthe same time that electrode E12 on the second lead 12 is activated as acathode.

In the illustrated embodiment, IPG 14 can individually control themagnitude of electrical current flowing through each of the electrodes.In this case, it is preferred to have a current generator, whereinindividual current-regulated amplitudes from independent current sourcesfor each electrode may be selectively generated. Although this system isoptimal to take advantage of the invention, other stimulators that maybe used with the invention include stimulators having voltage regulatedoutputs. While individually programmable electrode amplitudes areoptimal to achieve fine control, a single output source switched acrosselectrodes may also be used, although with less fine control inprogramming. Mixed current and voltage regulated devices may also beused with the invention. Further details discussing the detailedstructure and function of IPGs are described more fully in U.S. Pat.Nos. 6,516,227 and 6,993,384, which are expressly incorporated herein byreference.

It should be noted that rather than an IPG, the SCS system 10 mayalternatively utilize an implantable receiver-stimulator (not shown)connected to the neurostimulation leads 12. In this case, the powersource, e.g., a battery, for powering the implanted receiver, as well ascontrol circuitry to command the receiver-stimulator, will be containedin an external controller inductively coupled to the receiver-stimulatorvia an electromagnetic link. Data/power signals are transcutaneouslycoupled from a cable-connected transmission coil placed over theimplanted receiver-stimulator. The implanted receiver-stimulatorreceives the signal and generates the stimulation in accordance with thecontrol signals.

Referring now to FIG. 4, one exemplary embodiment of an RC 16 will nowbe described. As previously discussed, the RC 16 is capable ofcommunicating with the IPG 14, CP 18, or ETS 20. The RC 16 comprises acasing 50, which houses internal componentry (including a printedcircuit board (PCB)), and a lighted display screen 52 and button pad 54carried by the exterior of the casing 50. In the illustrated embodiment,the display screen 52 is a lighted flat panel display screen, and thebutton pad 54 comprises a membrane switch with metal domes positionedover a flex circuit, and a keypad connector connected directly to a PCB.In an optional embodiment, the display screen 52 has touchscreencapabilities. The button pad 54 includes a multitude of buttons 56, 58,60, and 62, which allow the IPG 14 to be turned ON and OFF, provide forthe adjustment or setting of stimulation parameters within the IPG 14,and provide for selection between screens.

In the illustrated embodiment, the button 56 serves as an ON/OFF buttonthat can be actuated to turn the IPG 14 ON and OFF. The button 58 servesas a select button that allows the RC 16 to switch between screendisplays and/or parameters. The buttons 60 and 62 serve as up/downbuttons that can be actuated to increment or decrement any ofstimulation parameters of the pulse generated by the IPG 14, includingpulse amplitude, pulse width, and pulse rate. For example, the selectionbutton 58 can be actuated to place the RC 16 in a “Pulse AmplitudeAdjustment Mode,” during which the pulse amplitude can be adjusted viathe up/down buttons 60, 62, a “Pulse Width Adjustment Mode,” duringwhich the pulse width can be adjusted via the up/down buttons 60, 62,and a “Pulse Rate Adjustment Mode,” during which the pulse rate can beadjusted via the up/down buttons 60, 62. Alternatively, dedicatedup/down buttons can be provided for each stimulation parameter. Ratherthan using up/down buttons, any other type of actuator, such as a dial,slider bar, or keypad, can be used to increment or decrement thestimulation parameters. Further details of the functionality andinternal componentry of the RC 16 are disclosed in U.S. Pat. No.6,895,280, which has previously been incorporated herein by reference.

Referring to FIG. 5, the internal components of an exemplary RC 16 willnow be described. The RC 16 generally includes a processor 64 (e.g., amicrocontroller), memory 66 that stores an operating program forexecution by the processor 64, as well as stimulation parameter sets,input/output circuitry, and in particular, telemetry circuitry 68 foroutputting stimulation parameters to the IPG 14 and receiving statusinformation from the IPG 14, and input/output circuitry 70 for receivingstimulation control signals from the button pad 54 and transmittingstatus information to the display screen 52 (shown in FIG. 4). As wellas controlling other functions of the RC 16, which will not be describedherein for purposes of brevity, the processor 64 generates newstimulation parameter sets in response to the user operation of thebutton pad 54. These new stimulation parameter sets would then betransmitted to the IPG 14 via the telemetry circuitry 68. Furtherdetails of the functionality and internal componentry of the RC 16 aredisclosed in U.S. Pat. No. 6,895,280, which has previously beenincorporated herein by reference.

As briefly discussed above, the CP 18 greatly simplifies the programmingof multiple electrode configurations, allowing the user (e.g., thephysician or clinician) to readily determine the desired stimulationparameters to be programmed into the IPG 14, as well as the RC 16. Thus,modification of the stimulation parameters in the programmable memory ofthe IPG 14 after implantation is performed by a user using the CP 18,which can directly communicate with the IPG 14 or indirectly communicatewith the IPG 14 via the RC 16. That is, the CP 18 can be used by theuser to modify operating parameters of the electrode array 26 near thespinal cord.

As shown in FIG. 2, the overall appearance of the CP 18 is that of alaptop personal computer (PC), and in fact, may be implemented using aPC that has been appropriately configured to include adirectional-programming device and programmed to perform the functionsdescribed herein. Alternatively, the CP 18 may take the form of amini-computer, personal digital assistant (PDA), etc., or even a remotecontrol (RC) with expanded functionality. Thus, the programmingmethodologies can be performed by executing software instructionscontained within the CP 18. Alternatively, such programmingmethodologies can be performed using firmware or hardware. In any event,the CP 18 may actively control the characteristics of the electricalstimulation generated by the IPG 14 to allow the optimum stimulationparameters to be determined based on patient feedback and forsubsequently programming the IPG 14 with the optimum stimulationparameters.

To allow the user to perform these functions, the CP 18 includes a mouse72, a keyboard 74, and a programming display screen 76 housed in a case78. It is to be understood that in addition to, or in lieu of, the mouse72, other directional programming devices may be used, such as atrackball, touchpad, joystick, or directional keys included as part ofthe keys associated with the keyboard 74.

In the illustrated embodiment described below, the display screen 76takes the form of a conventional screen, in which case, a virtualpointing device, such as a cursor controlled by a mouse, joy stick,trackball, etc., can be used to manipulate graphical objects on thedisplay screen 76. In alternative embodiments, the display screen 76takes the form of a digitizer touch screen, which may either passive oractive. If passive, the display screen 76 includes detection circuitrythat recognizes pressure or a change in an electrical current when apassive device, such as a finger or non-electronic stylus, contacts thescreen. If active, the display screen 76 includes detection circuitrythat recognizes a signal transmitted by an electronic pen or stylus. Ineither case, detection circuitry is capable of detecting when a physicalpointing device (e.g., a finger, a non-electronic stylus, or anelectronic stylus) is in close proximity to the screen, whether it bemaking physical contact between the pointing device and the screen orbringing the pointing device in proximity to the screen within apredetermined distance, as well as detecting the location of the screenin which the physical pointing device is in close proximity. When thepointing device touches or otherwise is in close proximity to thescreen, the graphical object on the screen adjacent to the touch pointis “locked” for manipulation, and when the pointing device is moved awayfrom the screen the previously locked object is unlocked.

As shown in FIG. 6, the CP 18 generally includes a controller/processor80 (e.g., a central processor unit (CPU)) and memory 82 that stores astimulation programming package 84, which can be executed by thecontroller/processor 80 to allow the user to program the IPG 14, and RC16. The CP 18 further includes output circuitry 86 (e.g., via thetelemetry circuitry of the RC 16) for downloading stimulation parametersto the IPG 14 and RC 16 and for uploading stimulation parameters alreadystored in the memory 66 of the RC 16, via the telemetry circuitry 68 ofthe RC 16. Notably, while the controller/processor 80 is shown in FIG. 6as a single device, the processing functions and controlling functionscan be performed by a separate controller and processor. Thus, it can beappreciated that the controlling functions described below as beingperformed by the CP 18 can be performed by a controller, and theprocessing functions described below as being performed by the CP 18 canbe performed by a processor.

Execution of the programming package 84 by the controller/processor 80provides a multitude of display screens (not shown) that can benavigated through via use of the mouse 72. These display screens allowthe clinician to, among other functions, to select or enter patientprofile information (e.g., name, birth date, patient identification,physician, diagnosis, and address), enter procedure information (e.g.,programming/follow-up, implant trial system, implant IPG, implant IPGand lead(s), replace IPG, replace IPG and leads, replace or reviseleads, explant, etc.), generate a pain map of the patient, define theconfiguration and orientation of the leads, initiate and control theelectrical stimulation energy output by the neurostimulation leads 12,and select and program the IPG 14 with stimulation parameters in both asurgical setting and a clinical setting. Further details discussing theabove-described CP functions are disclosed in U.S. patent applicationSer. No. 12/501,282, entitled “System and Method for Converting TissueStimulation Programs in a Format Usable by an Electrical CurrentSteering Navigator,” and U.S. patent application Ser. No. 12/614,942,entitled “System and Method for Determining Appropriate Steering Tablesfor Distributing Stimulation Energy Among Multiple NeurostimulationElectrodes,” which are expressly incorporated herein by reference.

Most pertinent to the present inventions, execution of the programmingpackage 84 provides a user interface that conveniently allows a user toprogram the IPG 14 using different programming modes, and in theillustrated embodiment, three programming modes: a manual programmingmode, an e-troll programming mode, and a Navigation programming mode.

Referring now to FIG. 7, a graphical user interface (GUI) 100 that canbe generated by the CP 18 to allow a user to program the IPG 14 will bedescribed. In the illustrated embodiment, the GUI 100 comprises threepanel: a program selection panel 102, a lead display panel 104, and anelectrical parameter adjustment panel 106. Some embodiments of the GUI100 may allow for closing and expanding one or both of the lead displaypanel 102 and the parameter adjustment panel 106 by clicking on the tab108 (to show or hide the parameter adjustment panel 106) or the tab 110(to show or hide the full view of both the lead selection panel 104 andthe parameter adjustment panel 106).

The program selection panel 102 provides information about programs andareas that have been, or may be, defined for the IPG 14. A plurality ofprograms may be displayed in carousel 112. In the illustratedembodiment, sixteen programs may be defined, but program 1 is the onlyone currently defined, as shown by the “1” in field 114. Otherembodiments may use a carousel or other techniques for displayingavailable programs with different numbers or arrangements of availableprogram slots.

Each program may be named, as indicated by the name field 116. Astimulation on/off button 118 allows turning the currently activeprogram on or off. When the active program is on, stimulation parametersets will be generated in the CP 18 and transmitted to the RC 16. Up tofour program areas 120 may be defined, allowing a program to controlstimulation of multiple areas. Each program area 120 may separatelycontrol stimulation of electrodes in the patient, and may be separatelyturned on or off. Each of the program areas 120 may be labeled with alabel 122 that may be used as a marker on the graphical leads 124 and126, as described below. A number of temporary areas 128 may be used fortemporary storage of area information by copying a program area 120 intoa temporary area 128 or copying a temporary area 128 into a program area120. This allows copying a program area 120 from one of the four slotsto another slot via one of the temporary areas 128. Other embodimentsmay also allow copying one of the program areas 120 into another one ofthe program areas 120 directly. Individual programs may be copied toother slots in the carousel 112 or deleted as desired.

Turning now to the lead display panel 104, graphical leads 124 and 126are illustrated with eight graphical electrodes 130 each (labeledelectrodes E1-E8 for lead 124 and electrodes E9-E16 for lead 126). Othernumbers of leads and electrodes per lead may be displayed as desired. Inan implanted system using other numbers of electrodes, that number ofelectrodes may be shown in lead display panel 104. Up to four groups ofleads may be viewed by selecting one of the lead group tabs 132. Inaddition, an icon 134 representing the case 44 of the IPG 14 isdisplayed in the lead display panel 104. In addition to allocatingcurrent to any of the electrodes of graphical leads 124 and 126, currentmay be allocated to the case 44 as an electrode.

Each of the electrodes 130 of the leads 124 and 126 may be individuallyselected, allowing the clinician to set the polarity and the magnitudeof the current allocated to that electrode 130. In the illustratedembodiment, electrode E15 is currently selected. Electrical current hasbeen allocated to three groups of electrodes respectively correspondingto three programming areas. Electrode group 130 a illustrates a singlecathode at electrode E2 to which is allocated 100% of the cathodiccurrent and two anodes at electrodes E1 and E3 to which are allocated25% and 75% of the anodic current, respectively. Electrode group 130 billustrates a single anode at electrode E7 to which is allocated 100% ofthe cathodic current and two anodes at electrodes E6 and E8 to which areallocated 50% and 50% of the anodic current, respectively. Electrodegroup 130 c illustrates a single anode at electrode E10 to which isallocated 100% of the cathodic current and two anodes at electrodes E9and E11 to which are allocated 60% and 40% of the anodic current,respectively.

The parameters adjustment panel 106 includes a pull-down programmingmode field 136 that allows the user to switch between the manualprogramming mode, the e-troll programming mode, and the Navigationprogramming mode. As shown in FIG. 7, the manual programming mode hasbeen selected. In the manual programming mode, each of the electrodes130 of the graphical leads 124 and 126, as well as the graphical case132, may be individually selected, allowing the clinician to set thepolarity (cathode or anode) and the magnitude of the current(percentage) allocated to that electrode 134 using graphical controlslocated in the amplitude/polarity area 138. In particular, a graphicalpolarity control 140 located in the area 138 includes a “+” icon, a “−”icon, and an “OFF” icon, which can be respectively actuated to togglethe selected electrode 134 between a positive polarization (anode), anegative polarization (cathode), and an off-state. An amplitude control142 in the area 138 includes an arrow that can be actuated to decreasethe magnitude of the fractionalized current of the selected electrode134, and an arrow that can be actuated to increase the magnitude of thefractionalized current of the selected electrode 134. The amplitudecontrol 142 also includes a display area that indicates the adjustedmagnitude of the fractionalized current for the selected electrode 134.Amplitude control 142 is preferably disabled if no electrode is visibleand selected in the lead display panel 104.

The parameters adjustment panel 106, when the manual programming mode isselected, also includes an equalization control 144 that can be actuatedto automatically equalize current allocation to all electrodes of apolarity selected by respective “Anode +” and “Cathode −” icons. Theparameters adjustment panel 106 also includes a pulse amplitudeadjustment control 150 (expressed in milliamperes (mA)), a pulse widthadjustment control 148 (expressed in microseconds (μs)), and a pulserate adjustment control 146 (expressed in Hertz (Hz)), which aredisplayed in all three of the programming modes. Each of the controls146, 148, 150 includes a first arrow that can be actuated to decreasethe value of the respective stimulation parameter and a second arrowthat can be actuated to increase the value of the respective stimulationparameter. Each of the controls 146, 148, 150 also includes a displayarea for displaying the currently selected parameter. In the illustratedembodiment, a pulse amplitude of 5 mA, a pulse width of 210 μs, a pulserate of 60 Hz have been selected. The controls 146, 148, 150 are alsodisplayed in

As shown in FIG. 8, the e-troll programming mode has been selected. Inthis mode, the electrodes 130 illustrated in the lead display panel 104that were individually selectable and configurable in manual programmingmode are used for display only and are not directly selectable orcontrollable. The parameter selection panel 106 includes a steeringarray of arrows 152 that allows steering the electrical current up,down, left, or right. In the illustrated embodiment, the electricalcurrent is steered by panning a virtual multipole (i.e., the virtualmultipole is moved relative to the actual electrodes 26 without changingthe basic configuration (focus (F) and upper anode percentage (UAP)) ofthe virtual multipole), and computing the electrical amplitude valuesneeded for the actual electrodes 26 to emulate the virtual multipole.For example, as shown in FIG. 9, a series of virtual multipoles, and inthis case, tripoles and bipoles, are sequentially defined in accordancewith a panned current steering technique over a plurality of dashedlines representing available electrode positions in the electrode array26.

In the illustrated embodiment, all of the virtual tripoles aresymmetrical in that the virtual anodes are equally spaced from thecentral virtual cathode. The nominal virtual multipoles can also beconsidered wide tripole/bipoles in that the virtual anode(s) are spaceda relatively large distance from the cathode (in this case, by twoelectrodes). Between the ends of the electrode array 26, a virtualtripole is panned along the electrode array 26 (i.e., the LGF value ismaintained as the virtual cathode is shifted along the electrode array26). However, as either of the outer virtual anodes of the virtualtripole abuts the last electrode in the array, a virtual bipole isutilized (upper virtual bipole at the top of the electrode array 26, anda lower virtual bipole at the bottom of the electrode array 26). Thevirtual bipole may then be panned along the electrode array 26 (i.e.,the LGF value is maintained as the virtual cathode is shifted along theelectrode array 26).

In the e-troll programming mode, the parameter adjustment panel 106 alsoincludes an advanced tab 154, which when actuated, hides the leaddisplay panel 104 and provides access to a resolution control 156 and afocus control 158, as shown in FIG. 10.

The resolution control 156 allows changing the stimulation adjustmentresolution. In one embodiment, three possible settings of Fine, Medium,and Coarse may be chosen. The resolution control 156 has a “+” icon anda “−” icon that can be used to adjust the resolution. The resolutioncontrol 156 also includes a display element that graphically displaysthe current resolution level. When the resolution is set to Fine, eachchange caused by use of the steering arrows 152 makes less of a changeto the electrode configuration than when the resolution is set to Mediumor Coarse. For example, panning of the virtual multipole with a Coarseresolution may displace the virtual multipole relative to the electrodearray 26 in steps equivalent to 10% of the electrode spacing, whereaspanning of the virtual multipole with a Fine resolution may move thevirtual multipole relative to the electrode array 26 in steps equivalentto 1% of the electrode spacing.

The focus control 158 allows changing the stimulation focus bydisplacing the anode(s) and cathode of the virtual multipole toward eachother to increase the focus, or displacing the anode(s) and cathode ofthe virtual multipole away from each other to decrease the focus. Thefocus control 158 has a “+” icon and a “−” icon that can be used toadjust the focus. The focus control 158 also includes a display elementthat graphically displays the current focus level.

As shown in FIG. 11, the Navigation programming mode has been selected.As in the e-troll programming mode, in the Navigation programming mode,the electrodes illustrated in the lead display panel 104 that wereindividually selectable and configurable in manual programming mode areused for display only and are not directly selectable or controllable.The parameter selection panel 106 includes a steering array of arrows162 that allows steering the electrical current up, down, left, orright. In the illustrated embodiment, the electrical current is steeredby weaving one or more anodes around the cathode of the virtualmultipole as the cathode is displaced relative to the electrode array26, and computing the electrical amplitude values needed for theelectrodes 26 to emulate the virtual multipole.

For example, as shown in FIG. 12, a series of virtual multipoles aresequentially defined in accordance with a weaved current steeringtechnique over a plurality of dashed lines representing availableelectrode positions in the electrode array 26. Each illustratedmultipole has a designator indicating whether it is a tripole or bipole(T for tripole and B for bipole), a subscripted designator indicatingthe longitudinal focus (LGF) in terms of electrode separation, and, inthe case of a bipole, a subscripted designator indicating the bipole isan upper bipole (u), meaning that the anode is above the cathode, or thebipole is a lower bipole (I), meaning that the anode is below thecathode.

In the embodiment illustrated in FIG. 12, the different virtualmultipoles are sequentially defined in the following order: a narrowvirtual tripole (T₂), a narrow upper virtual bipole (B_(2u)), a wideupper virtual bipole (B_(3u)), a wide virtual tripole (T_(2.5)), a widelower virtual bipole (B_(3l)), a narrow lower virtual bipole (B_(2l)),and the narrow virtual tripole (T₂). For purposes of this specification,the terms “narrow” and “wide,” when used together to define a virtualbipole or a virtual tripole in either the e-troll programming mode orthe Navigation programming mode, are relative terms, and simply meanthat the narrow bipole and/or narrow tripole have longitudinal focuses(LGFs) that are less than the longitudinal focuses (LGFs) of the widebipole and/or wide tripole.

The virtual multipoles illustrated in FIG. 12 may be considered criticalpoints between which the cathode position and longitudinal focus (LGF)are incrementally changed by mapping the sequences in a “weave space,”defined by the longitudinal focus (LGF) and the upper anode percentage(UAP). As best shown in FIG. 13, the sequence of virtual multipoles isdefined by a trajectory line sequentially connecting the critical points(representing by circles) that provides a continuous change in thevirtual multipoles.

As can be seen from FIG. 13, the sequence beginning with the narrowvirtual tripole (T₂) and ending with the narrow upper virtual bipole(B_(2u)) incrementally increases the upper anode percentage (UAP) whilemaintaining the longitudinal focus (LGF). The sequence beginning withthe narrow upper virtual bipole (B_(2u)) and ending with the wide uppervirtual bipole (B_(3u)) maintains the upper anode percentage (UAP) whileincrementally increasing the longitudinal focus (LGF). The sequencebeginning with the wide upper virtual bipole (B_(3u)) and ending withthe wide virtual tripole (T_(2.5)) incrementally decreases the upperanode percentage (UAP) while incrementally decreasing the longitudinalfocus (LGF). The sequence beginning with the wide virtual tripole(T_(2.5)) and ending with the wide lower virtual bipole (B_(3l))incrementally decreases the upper anode percentage (UAP) whileincrementally increasing the longitudinal focus (LGF). The sequencebeginning with the wide lower virtual bipole (B_(3l)) and ending withthe narrow lower virtual bipole (B_(2l)) maintains the upper anodepercentage (UAP) while incrementally decreasing the longitudinal focus(LGF). The sequence beginning with the narrow lower virtual bipole(B_(2l)) and ending with the narrow virtual tripole (T₂) incrementallyincreases the upper anode percentage (UAP) while maintaining thelongitudinal focus (LGF).

Notably, the above-mentioned sequence maintains the same position of thevirtual cathode relative to the electrode array 26 while transitioningthrough different types of virtual bipole/tripoles between the narrowvirtual tripole (T₂) and the wide upper virtual bipole (B_(3u)),incrementally changes the position of the virtual cathode relative tothe electrode array 26 in one direction (in this case, upward) betweenthe wide upper virtual bipole (B_(3u)) and the wide lower virtual bipole(B_(3l)), and the maintains the same position of the virtual cathoderelative to the electrode array 26 while transitioning through differenttypes of virtual bipole/tripoles between the wide lower virtual bipole(B_(3l)) and the narrow virtual tripole (T₂). The sequence illustratedin FIG. 12 can be repeatedly cycled through, with the effect being thatthe virtual cathode is shifted upward by one electrode per each cycle.Further details discussing various weaved current steering techniquesare described in U.S. Provisional Patent Application Ser. No.61/452,965, entitled “Neurostimulation System for Defining a GeneralizedVirtual Multipole,” which has previously been incorporated herein byreference.

In the Navigation programming mode, the parameter adjustment panel 106also includes the previously described advanced tab 154, which whenactuated, hides the lead display panel 104 provides access to theresolution control 156 and the focus control 158 in the same mannerdescribed above with respect to the e-troll programming mode in FIG. 10.

The resolution control 156 allows changing the stimulation adjustmentresolution. In one embodiment, three possible settings of Fine, Medium,and Coarse may be chosen. When the resolution is set to Fine, eachchange caused by use of the steering arrows 162 makes less of a changeto the electrode configuration than when the resolution is set to Mediumor Coarse. In particular, depending on the resolution, different stepsizes may be used transition between the virtual multipoles illustratedin FIG. 12. For example, if the resolution is set to be Fine, a fineresolution (10 steps per critical point transition) may be used totransition between the critical points where the cathode is not beingshifted, and an even finer resolution (20 steps per critical pointtransition) may be used to transition between the critical points wherethe cathode is being shifted. If the resolution is set to be Coarse, acoarse resolution (5 steps per critical point transition) may be used totransition between all of the critical points.

The focus control 158 allows changing the stimulation focus bydisplacing the anode(s) and cathode of each of the virtual multipolestoward each other to increase the focus, or displacing the anode(s) andcathode of each of the virtual multipoles away from each other todecrease the focus.

The CP 18 may transition between different programming modes usingtechniques disclosed in U.S. Provisional Patent Application Ser. No.61/576,924, entitled “Seamless Integration of Different ProgrammingModes for a Neurostimulator Programming System,” which is expresslyincorporated herein by reference.

As discussed in the background, it is desirable to steer the electricalcurrent in a manner that transitions the resulting electrical field assmoothly as possible. To this end, the CP 18 utilizes a Heuristic SafetyNet (HSN) that ensures that comfortable and efficacious therapy ismaintained as each virtual multipole is transitioned to the next virtualmultipole. Referring to FIG. 14, one method of using an HSN whensteering current will now be described.

First, the CP 18 defines an immediate virtual multipole (step 200),defines a immediate fractionalized electrode configuration that emulatesthe immediate virtual multipole (step 202), and instructs the IPG 14 toconvey electrical energy to the electrodes 26 in accordance with theimmediate fractionalized electrode configuration (step 204). In responseto actuation of any of the steering arrows in the GUI 100 (steeringarrows 152 when in the E-troll programming mode or steering arrows 162when in the Navigation programming mode), the CP 18 defines a newvirtual multipole by changing a parameter of the immediate virtualmultipole by a step size (step 206) and defines a new fractionalizedelectrode configuration that emulates the new virtual multipole (step208). In the illustrated embodiment, the new virtual multipole can becomputed in accordance with the equation: X_(new)=X_(current)+ΔX orX_(new)=X_(current)−ΔX, where X_(new) is the parameter of the newvirtual multipole, X_(current) is the parameter of the immediate virtualmultipole, and ΔX is the step size. Thus, the parameter of the immediatevirtual multipole can be either increased by the step size or decreasedby the step size to generate the new virtual multipole.

The parameter may be, e.g., an x-y location of the virtual multipole(e.g., in the case where the virtual multipole is panned in the e-trollprogramming mode) or a focus or upper anode percentage (e.g., in thecase where the virtual multipole is weaved in the Navigation programmingmode). The step size(s) of the parameter may be adjusted, e.g., via theresolution control 156. In some cases, such as when in the Navigationprogramming mode, the CP 18 may define the new virtual multipole byrespectively changing multiple parameters (e.g., the focus and upperanode percentage) of the immediate virtual multipole by a multiple ofstep sizes.

Next, the CP 18 computes one or more difference values as a function ofthe immediate virtual multipole and the new virtual multipole (step 210)and respectively compares the difference value(s) to one or more limitvalue(s) (step 212). In the illustrated embodiment, the differencevalue(s) is a function of the immediate fractionalized electrodeconfiguration and the new fractionalized electrode configuration. In analternative embodiment, the difference value(s) is a function of one ormore of an electrical field, absolute potential, current density, anactivating function, a total net driving function, etc. derived from theimmediate virtual multipole and the new virtual multipole. In anotheralternative embodiment, the difference value may be a displacementbetween one pole (e.g., the virtual cathode) of the immediate virtualmultipole and a corresponding pole of the new virtual multipole.

In the case where the difference value(s) is a function of the immediatefractionalized electrode configuration and the new fractionalizedelectrode configuration, the difference value(s) may be, e.g., a changein a fractionalized cathodic current on an individual one of theelectrodes 26 (CI) (e.g., if the cathodic current on electrode E2changes from 5% to 15%, the difference value will be 10%), a change in afractionalized anodic current on an individual one of the electrodes 26(AI) (e.g., if the anodic current on electrode E8 changes from 50% to30%, the difference value will be 20%), a total fractionalized change incathodic current on the electrodes 26 (CT) (e.g., if the cathodiccurrent on electrode E1 changes from 10% to 20%, the cathodic current onelectrode E2 changes from 30% to 20%, and the cathodic current on theremaining electrodes remains the same, the difference value will be20%), and/or a total fractionalized change in anodic current on theelectrodes 26 (AT) (e.g., if the anodic current on electrode E7 changesfrom 20% to 25%, and the anodic current on electrode E8 changes from 35%to 30%, and the anodic current on the remaining electrodes remains thesame, the difference value will be 10%). The limit values may be, e.g.,in the range of 5-50% for CI, 5-80% for AI, 10-90% for CT, and 10-90%for AT. In the illustrated embodiment, all of the electrodes 26 areconsidered when comparing the different value(s) to the respective limitvalue(s). In an alternative embodiment, less than all of the electrodesmay be considered when comparing the different value(s) to therespective limit value(s).

Next, the CP 18 compares the difference value(s) to the respective limitvalue(s) (step 214). If none of the difference value(s) exceeds therespective limit value, the CP 18 instructs the IPG 14 to conveyelectrical energy to the electrodes 26 in accordance with the newfractionalized electrode configuration (step 216). If any of thedifferent value(s) exceeds the respective limit value, the CP 18 doesnot instruct the IPG 14 to convey electrical energy to the electrodes26, but instead determines whether the number of times the differencevalue(s) have been compared to the respective limit value(s) hasexceeded a maximum number of iterations (e.g., in the range of 2-20iterations) (step 218). If the maximum number of iterations has beenexceeded, the CP 18 returns an error message to the user indicating such(step 220). If the maximum number of iterations has not been exceeded,the CP 18 decreases the absolute value of the step size to create a newstep size (step 222), and then repeats steps 206-218 for the new stepsize. The absolute value of the step size can be decreased in accordancewith the equation ΔX_(new)=ΔX_(current)·K, where ΔX_(new) is the newstep size, ΔX_(current) is the current step size, and K is amultiplication factor that is less than 1. In the case where multipleparameters are used to generate the new virtual multipole, all of thestep sizes associated with these multiple parameters may be decreased.

Referring to FIGS. 15A and 15B, another method of using an HSN whensteering current will now be described. In this method, an HSN isemployed to define and apply electrode configuration transitions betweenan immediate electrode configuration and a final electrodeconfiguration. With reference first to FIG. 15A, the CP 18 defines animmediate (initial) electrode configuration, which may be afractionalized electrode configuration as discussed above (step 302),and instructs the IPG 14 to convey electrical energy to the electrodes26 in accordance with the immediate fractionalized electrodeconfiguration (step 304).

In response to actuation of any of the steering arrows in the GUI 100(steering arrows 152 when in the E-troll programming mode or steeringarrows 162 when in the Navigation programming mode), the CP 18 defines anew (final) electrode configuration (step 306). To proceed from theexisting initial configuration to the defined final configuration, theCP 18 defines a series of intermediate electrode configurations, and inparticular, repeatedly defines a next intermediate electrodeconfiguration based on an immediate previously defined electrodeconfiguration and the final electrode configuration until the nextintermediate electrode configuration matches the final electrodeconfiguration (steps 308-314). In the illustrated embodiment, each nextintermediate electrode configuration is defined by shifting anodicand/or cathodic current from the immediate previously defined electrodeconfiguration to the next intermediate electrode configuration until theintermediate electrode configuration matches the final electrodeconfiguration.

The heuristic set of rules limits shifting of the anodic and/or cathodiccurrent from the immediate previously defined electrode configuration tothe next intermediate electrode configuration based on, e.g., a maximumchange in a fractionalized cathodic current on an individual one of theelectrodes 26 (e.g., a maximum cathodic current change in the range of5-50%), a maximum change in a fractionalized anodic current on anindividual one of the electrodes 26 (e.g., a maximum anodic currentchange in the range of 5-80%), a total fractionalized change in cathodiccurrent on the electrodes 26 (e.g., a maximum cathodic current change inthe range of 10-90%), and a total fractionalized change in anodiccurrent on the electrodes 26 (e.g., a maximum cathodic current change inthe range of 10-90%). In the illustrated embodiment, all of theelectrodes 26 are considered when comparing the different value(s) tothe respective limit value(s). In an alternative embodiment, less thanall of the electrodes may be considered when comparing the differentvalue(s) to the respective limit value(s).

While considering the maximum current change limits discussed above, theCP 18 defines the next intermediate electrode configuration based onelectrical current transitions between the electrodes of the immediatepreviously defined electrode configuration and the respective electrodesof the final electrode configuration. In this embodiment, a “transition”refers to a change in the electrical current being applied to individualelectrodes in an electrode configuration. Thus, a transition can be a nocurrent change transition, a cathodic current increase transition, acathodic current decrease transition, a cathodic current decrease/anodiccurrent increase transition, an anodic current increase transition, ananodic current decrease transition, and an anodic currentdecrease/cathodic current increase transition.

In order to understand how the heuristic rules can be applied usingelectrical current transitions between the immediate previously definedelectrode configuration and the final electrode configuration, anexemplary set of heuristic rules will now be described with respect toFIG. 15B.

For ease of reference, as illustrated in box 402, specific electricalcurrent transitions are assigned numeric designators 1-6, and inparticular, 0=no current change; 1=cathodic current increase; 2=cathodiccurrent decrease; 3=cathodic current decrease/anodic current increase;4=anodic current increase; 5=anodic current decrease; and 6=anodiccurrent decrease/cathodic current increase. These designators will beexclusively employed in the following discussion. Thus, a transitionfrom one electrode configuration to a second electrode configuration canbe characterized completely by identifying the current changes for eachelectrode.

Moreover, it has been noted that certain combinations of currenttransitions for a pair of electrodes naturally occur when transitioningcurrent (i.e., when current is changed for one electrode to effect aspecific current transition, the current is naturally changed foranother electrode to effect a different current transition). Suchcombinations are termed “Natural Direction Combinations,” and are setout in box 404. As can be seen there, a first natural combination is thecombination of transitions 1 and 2; that is, an increase in cathodiccurrent for one electrode coupled with a decrease in cathodic currentfor the other electrode. A second natural combination is the combinationof transitions 1 and 3; that is, an increase in cathode current for oneelectrode coupled with an increase in cathodic current/decrease inanodic current for the other electrode. A third natural combination isthe combination of transitions of 4 and 5; that is, an increase inanodic current for one electrode coupled with a decrease in anodiccurrent for the other electrode. A fourth natural combination is thecombination of transitions of 4 and 6; that is, an increase in anodiccurrent for one electrode coupled with a decrease in anodiccurrent/increase in cathodic current for the other electrode.

The heuristic rules embodied in FIG. 15B can generally be described asfollows. The decision blocks 406, 408, 416, and 422 inquire into thenature of the current transitions required between the previouslydefined intermediate electrode configuration and the final electrodeconfiguration, and action blocks 410, 412, 414, 418, 420, 424, and 426govern the current transitions to be achieved based on these inquiries,and subject to the maximum limits discussed above.

The first inquiry is whether all of the electrodes either require atransition 3 or a transition 6 (step 406). If not all of the electrodeseither require a transition 3 or a transition 6, it is determinedwhether any of the four natural direction combinations shown in box 604exist (step 408).

If any of the four natural direction combinations exists, current isshifted in accordance with the natural direction combinations in thefollowing order. If a natural combination of transitions 4 and 6 exists,anodic current is shifted from the electrode having the transition 6 tothe electrode having the transition 4 (essentially attempting toeliminate the transition 6 from the electrode configuration) (step 410).If a natural combination of transitions 1 and 3 exists, cathodic currentis shifted from the electrode having the transition 3 to the electrodehaving the transition 1 (essentially attempting to eliminate thetransition 3) (step 412). If any other natural combination oftransitions exists, cathodic current is shifted from the electrodehaving the transition 2 to the electrode having the transition 1 in thecase where the natural combination of transitions 1 and 2 exists, andanodic current is shifted from the electrode having the transition 5 tothe electrode having the transition 4 in the case where the naturalcombination of transitions 4 and 5 exists (step 414).

If none of the four natural direction combinations exists, it isdetermined whether there exists an electrode having a transition 6, andanother electrode having either a transition 0 or a transition 5 (step416). If so, anodic current is shifted from the electrode having thetransition 6 to the electrode having the transition 0 or 5 (essentiallyconverting the transition 6 to the transition 1) (step 418). If not,cathodic current is shifted from an electrode having a transition 3 toan electrode having a transition 0 or an electrode having a transition 2(essentially converting the transition 3 to the transition 4) (step420).

If all of the electrodes either require a transition 3 or a transition 6at step 608, it determined whether there exists multiple electrodeshaving a transition 6 (step 422). If so, anodic current is shifted fromthe electrode having the greatest cathodic current for the finalelectrode configuration to another electrode (essentially converting atransition 6 to a transition 1) (step 424). If not, cathodic current isshifted from any cathodic electrode in the previous intermediateelectrode configuration to the electrode having the greatest cathodiccurrent in the previous intermediate electrode configuration(essentially converting a transition 3 to a transition 4) (step 426).

The set of heuristic rules embodied in FIGS. 15A and 15B can thus bestated as follows:

Rule 1: Determine whether all of the electrodes either have a cathodiccurrent decrease/anodic current increase transition (transition 3) or ananodic current decrease/cathodic current decrease transition (transition6), and if not, go to Rules 2-7, and if so, go to Rules 8-9.

Rule 2: Determine whether a first electrode pairing exists, having acathodic current increase transition (transition 1) and a cathodiccurrent decrease transition (transition 2). If so, shift cathodiccurrent from the electrode having the cathodic current decreasetransition (transition 2) to the electrode having the cathodic currentincrease transition (transition 1).

Rule 3: Determine whether a second electrode pairing exists having acathodic current increase transition (transition 1) and a cathodiccurrent decrease/anodic current increase transition (transition 3). Ifso, shift, cathodic current from the electrode having the cathodiccurrent decrease/anodic current increase transition (transition 3) tothe electrode having the cathodic current increase transition(transition 1).

Rule 4: Determine whether a third electrode pairing exists having ananodic current increase transition (transition 4) and an anodic currentdecrease transition (transition 5). If so, shift anodic current from theelectrode having the anodic current decrease transition (transition 5)to the electrode having the anodic current increase transition(transition 4).

Rule 5: Determine whether a fourth electrode pairing having an anodiccurrent increase transition (transition 4) and an anodic currentdecrease/cathodic current increase transition (transition 6). If so,shift, anodic current from the electrode having the anodic currentdecrease/cathodic current increase transition (transition 6) to theelectrode having the anodic current increase transition (transition 40.

Rule 6: If none of the first through fourth electrode pairings exist,determine whether a first electrode exists having an anodic currentdecrease/cathodic current increase transition (transition 6) and whethera second electrode exists having either a no current change transition(transition 0) or an anodic current decrease transition (transition 5).If so, shift anodic current from the first electrode to the secondelectrode.

Rule 7: If either the first electrode or the second electrode does notexist, shift cathodic current from an electrode having a cathodiccurrent decrease/anodic current increase transition to an electrodehaving either a no current change transition or a cathodic currentdecrease transition.

Rule 8: If all of the electrodes either have a cathodic currentdecrease/anodic current increase transition (transition 3) or an anodiccurrent decrease/cathodic current increase transition (transition 6),and if there exists multiple electrodes each having an anodic currentdecrease/cathodic current increase transition (transition 6), determinewhich one of the multiple electrodes has the greatest cathodic currentfor the final electrode configuration, and shift anodic current from theone electrode to another electrode.

Rule 9: If the multiple electrodes do not exist, determine one electrodehaving the greatest cathodic current for the previous intermediateelectrode configuration, and shift cathodic current from any electrodehaving cathodic current for the previous intermediate electrodeconfiguration to the one electrode.

It will be understood that the application of heuristic rules, and theheuristic rules themselves, set out in the discussion above, areexemplary in nature. The empirical nature of the heuristic rulesthemselves suggests that further investigation could result in differentrules, changes in the substantive nature of the rules themselves cannotaffect the scope of the invention set out and claimed herein.

Referring now to FIG. 16, an example will now be discussed, employingthe set of heuristic rules set out above. The diagram illustratestransitions between electrode configurations for a set of fiveelectrodes, A-E, at five successive times T1-T5. Arrows represent shiftsof fractionalized current from one electrode to another electrode, andnumbers beside the arrow represent magnitude of change in thefractionalized current. Each intermediate electrode configurationbecomes the becomes the starting point for the next intermediateelectrode configuration. The numbers below each electrode box correspondto the current transition (specified in box 402 of FIG. 15B) requiredfor that electrode to make the transition from an intermediate electrodeconfiguration to the final electrode configuration. Here, a change infractional current on any specific electrode (whether cathodic oranodic) is 40 percentage points.

Rules 1 and 4 are implemented for the intermediate electrodeconfiguration at time T1, where not all of the electrodes havetransitions 3 and 6, and there is a natural direction combination inthat electrode C has 60% of the anodic current and a required transition6 to make electrode C have 40% of the cathodic current in the finalelectrode configuration at time T5, and electrode E has 0% current and arequired transition 4 to make electrode E have 40% of the anodic currentin the final electrode configuration at time T5. In this case, 40% ofthe anodic current is shifted from electrode C to electrode E, resultingin an intermediate electrode configuration at time T2 where electrodes Cand E respectively now have anodic currents of 20% and 40%. There are noother natural direction combinations for the intermediate electrodeconfiguration at time T1.

Rules 1 and 6 are implemented for the intermediate electrodeconfiguration at time T2, where not all of the electrodes havetransitions 3 and 6, there are no natural direction combinations, andelectrode C has 20% of the anodic current and a required transition 6 tomake electrode C have 40% of the cathodic current in the final electrodeconfiguration at time T5, and electrode E has 40% of the anodic currentand a required transition 0 to make electrode E have 40% of the anodiccurrent in the final electrode configuration at time T5. In this case,20% of the anodic current is shifted from electrode C to electrode E,resulting in an intermediate electrode configuration at time T3 whereelectrodes C and E respectively now have a current of 0% and an anodiccurrent of 60%.

Rules 1 and 3 are implemented for the intermediate electrodeconfiguration at time T3, where not all of the electrodes havetransitions 3 and 6, and there is a natural direction combination inthat electrode B has 20% of the cathodic current and a requiredtransition 3 to make electrode B have 40% of the anodic current in thefinal electrode configuration at time T5, and electrode C has 0% currentand a required transition 1 to make electrode C have 40% of the cathodiccurrent in the final electrode configuration at time T5. In this case,20% of the cathodic current is shifted from electrode B to electrode C,resulting in an intermediate electrode configuration at time T4 whereelectrodes B and C respectively now have a current of 0% and a cathodiccurrent of 20%. There are no other natural direction combinations forthe intermediate electrode configuration at time T1.

Rules 1, 2, and 4 are implemented for the intermediate electrodeconfiguration at time T4, where not all of the electrodes havetransitions 3 and 6, and there is a first natural direction combinationin that electrode A has 80% of the cathodic current and a requiredtransition 2 to make electrode A have 60% of the cathodic current in thefinal electrode configuration at time T5, and electrode C has 20% of thecathodic current and a required transition 1 to make electrode C have40% of the cathodic current in the final electrode configuration at timeT5, and a second natural direction combination in that electrode B has0% current and a required transition of 4 to make electrode B have 40%of the anodic current, electrode D has 40% of the anodic current and arequired transition of 5 to make electrode D have 20% of the anodiccurrent in the final electrode configuration at time T5, and electrode Ehas 60% of the anodic current and a required transition of 5 to makeelectrode E have 40% of the anodic current in the final electrodeconfiguration. In this case, 20% of the cathodic current is shifted fromelectrode A to electrode C, resulting in the desired final electrodeconfiguration at time T5 where electrodes A and C respectively have acathodic current of 60% and a cathodic current of 40%, and 20% of theanodic current is shifted from electrode D to electrode B, and 20% ofthe anodic current is shifted from electrode E to electrode B, resultingin the desired final electrode configuration at time T5 where electrodesB, D, and E respective have an anodic current of 40%, an anodic currentof 20%, and an anodic current of 40%.

With reference to FIG. 17, in another example, rules 1 and 8 areimplemented for the intermediate electrode configuration at time T1,where all of the electrodes have transitions 3 and 6, there are multipleelectrodes with transitions 6, and all of the anodic current must beshifted from the electrode having the largest cathodic current for thefinal electrode configuration. In this case, electrode C has thegreatest cathodic current for the final electrode configuration at 50%,and thus, 20% of the anodic current is shifted from electrode C toelectrode A, and 20% of the anodic current is shifted from electrode Cto electrode D, resulting in an intermediate electrode configuration attime T2 where electrodes A, C, and D respectively now have anodiccurrents of 30%, 20%, and 50%. Notably, since the maximum current thatcan be shifted to or from any individual electrode is 40% for eachtransition, and electrode C had an anodic current of 60% at time T1, anadditional 20% of the anodic current must be shifted from electrode C,in which case, 10% of the anodic current is shifted from electrode C toelectrode A, and 10% of the anodic current is shifted from electrode Cto electrode D, resulting in an intermediate electrode configuration attime T3 where electrodes A, C, and D respectively now have anodiccurrents of 40%, 0%, and 60%. For the remaining intermediate electrodeconfigurations at times T3-T9, rules 2-5 are implemented to shiftcurrent between natural direction combinations, resulting in the finalelectrode configuration at time T10.

With reference to FIG. 18, in still another example, rules 1 and 9 areimplemented for the intermediate electrode configuration at time T1,where all of the electrodes have transitions 3 and 6, there is only oneelectrode with a transition 6, all cathodic current must be consolidatedto the electrode having the largest cathodic current. In this case,electrode E has the greatest cathodic current for the intermediateelectrode configuration at time T1 at 40%, and thus, 10% of the cathodiccurrent is shifted from electrode A to electrode E, 20% of the cathodiccurrent is shifted from electrode B to electrode E, and 10% of thecathodic current is shifted from electrode D to electrode E, resultingin an intermediate electrode configuration at time T2 where electrodesA, B, D, and E respectively now have cathodic currents of 0%, 0%, 20%,and 80%. Notably, since the maximum current that can be shifted to orfrom any individual electrode is 40% for each transition, and 60% of thecathodic current must be shifted to electrode E to consolidate all ofthe cathodic current in one electrode, an additional 20% of the cathodiccurrent must be shifted to electrode E1, in which case, 20% of theremaining current on electrode D is shifted to electrode E, resulting inan intermediate electrode configuration at time T3 where electrodes Dand E respectively now have cathodic currents of 0% and 100%, therebyeffecting full consolidation of the cathodic current in one electrode.For the remaining intermediate electrode configurations at times T3-T9,rules 2-5 are implemented to shift current between natural directioncombinations, resulting in the final electrode configuration at timeT10.

With reference to FIG. 19, in another example, rules 1, 6, and 7 areimplemented for the intermediate electrode configuration at time T1,where not all of the electrodes have transitions 3 and 6, there are nonatural direction combinations, and there are no electrodes withtransitions of 0 or 5, and the cathodic current must be shifted from theelectrode having a transition of 3 to the electrodes with transitions of0 or 2. In this case, electrode E has a transition of 3, and electrodesB and D have transitions of 0, and thus, 20% of the cathodic current isshifted from electrode E to electrode B, and 20% of the cathodic currentis shifted from electrode E to electrode D, resulting in an intermediateelectrode configuration at time T2 where electrodes B, D, and Erespectively now have cathodic currents 20%, 30%, and 50%. Notably,since the maximum current that can be shifted to or from any individualelectrode is 40% for each transition, and electrode E had a cathodiccurrent of 50% at time T1, an additional 10% of the cathodic currentmust be shifted from electrode C, in which case, 5% of the cathodiccurrent is shifted from electrode E to electrode B, and 5% of thecathodic current is shifted from electrode E to electrode B, resultingin an intermediate electrode configuration at time T3 where electrodesB, D, and E respectively now have cathodic currents of 40%, 50%, and10%. For the remaining intermediate electrode configurations at timesT3-T6, rules 2-5 are implemented to shift current between naturaldirection combinations, resulting in the final electrode configurationat time T7.

Although particular embodiments of the present disclosure have beenshown and described, it will be understood that it is not intended tolimit the present disclosure to the preferred embodiments, and it willbe obvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present disclosure. Thus, the present disclosure are intended tocover alternatives, modifications, and equivalents, which may beincluded within the spirit and scope of the present disclosure asdefined by the claims.

What is claimed is:
 1. A system for an electrical neurostimulatorcoupled to a plurality of electrodes, comprising: a user interfaceconfigured for receiving a user input; and a controller/processorconfigured for (a) defining an immediate virtual multipole, (b) definingan immediate electrode configuration that emulates the immediate virtualmultipole, (c) defining a new virtual multipole by changing a parameterof the immediate virtual multipole by a step size in response to theuser input, (d) defining a new electrode configuration that emulates thenew virtual multipole, (e) computing a difference value as a function ofthe immediate virtual multipole and the new virtual multipole, (f)comparing the difference value to a limit value, (g) decreasing theabsolute value of the step size to create a new step size, and (h)repeating steps (c)-(f) for the new step size.
 2. The system of claim 1,further comprising (g) instructing the electrical neurostimulator toconvey electrical energy to the plurality of electrodes in accordancewith the new electrode configuration after steps (c)-(f) have beenrepeated.
 3. The system of claim 1, wherein the controller/processor isconfigured for (g) not instructing the electrical neurostimulation toconvey electrical energy to the plurality of electrodes in accordancewith the new electrode configuration before steps (c)-(f) have beenrepeated.
 4. The system of claim 1, wherein the controller/processor isconfigured for (c) defining the new virtual multipole by changing atleast one other parameter of the immediate virtual multipole by anotherstep size, and (g) decreasing the absolute value of the other step sizeto create another new step size, and repeating steps (c)-(f) for the newstep size and the other new step size.
 5. The system of claim 1, whereinthe parameter comprises one of a location, focus, and upper anodepercentage of the immediate virtual multipole.
 6. The system of claim 1,wherein the step size is one of a positive value and a negative value.7. The system of claim 1, wherein the controller/processor is configuredfor (e) computing another difference value as another function of theimmediate virtual multipole and the new virtual multipole, (f) comparingthe other difference value to another limit value, and (g) decreasingthe absolute value of the step size to create the new step size.
 8. Thesystem of claim 1, wherein the difference value is a function of theimmediate electrode configuration and the new electrode configuration.9. The system of claim 8, wherein the difference value comprises one ofa change in a cathodic current on an individual one of the electrodes, achange in an anodic current on an individual one of the electrodes, atotal change in cathodic current on the electrodes, and a total changein anodic current on the electrodes.
 10. The system of claim 1, whereinthe difference value is a function of one of an electrical field,absolute potential, current density, an activating function, and a totalnet driving function that is derived from the immediate virtualmultipole and the new virtual multipole.
 11. The system of claim 1,wherein the difference value is a displacement between one pole of theimmediate virtual multipole and a corresponding pole of the new virtualmultipole.
 12. The system of claim 1, further comprising telemetrycircuitry configured for communicating with the electricalneurostimulator, wherein the controller/processor is further configuredfor instructing the electrical neurostimulator via the telemetrycircuitry to convey electrical energy to the plurality of electrodes inaccordance with the immediate electrode configuration.
 13. The system ofclaim 1, wherein the immediate and new electrode configurations arerespectively immediate and new fractionalized combinations.
 14. Thesystem of claim 1, further comprising a housing containing the userinterface and the controller/processor.
 15. A method of providingtherapy to a patient using a plurality of electrodes, comprising: (a)defining an immediate virtual multipole; (b) defining an immediateelectrode configuration that emulates the immediate virtual multipole;(c) receiving an input from a user; (d) defining a new virtual multipolein response to the user input by changing a parameter of the immediatevirtual multipole by a step size; (e) defining a new electrodeconfiguration that emulates the new virtual multipole; (f) computing adifference value as a function of the immediate virtual multipole andthe new virtual multipole; (g) comparing the difference value to a limitvalue; (h) decreasing the absolute value of the step size to create anew step size, and repeating steps (c)-(g) for the new step size. 16.The method of claim 15, further comprising (i) conveying electricalenergy to the plurality of electrodes in accordance with the newelectrode configuration after steps (c)-(g) have been repeated.
 17. Themethod of claim 15, further comprising (i) not instructing theelectrical neurostimulation to convey electrical energy to the pluralityof electrodes in accordance with the new electrode configuration beforesteps (c)-(g) have been repeated.
 18. The method of claim 15, wherein:(d) the new virtual multipole is defined by changing another parameterof the immediate virtual multipole by another step size; and (h) theabsolute value of the other step size is decreased to create another newstep size, and steps (c)-(g) are repeated for the new step size and theother new step size if the difference value exceeds the limit value. 19.The method of claim 15, wherein the parameter comprises one of alocation, focus, and upper anode percentage of the immediate virtualmultipole.
 20. The method of claim 15, wherein the step size is one of apositive value and a negative value.
 21. The method of claim 15,wherein: (f) another difference value is computed as another function ofthe immediate virtual multipole and the new virtual multipole; (g) theother difference value is compared to another limit value; and (h) theabsolute value of the step size is decreased to create the new stepsize.
 22. The method of claim 14, wherein the difference value is afunction of the immediate electrode configuration and the new electrodeconfiguration.
 23. The method of claim 22, wherein the difference valuecomprises one of a change in a cathodic current on an individual one ofthe electrodes, a change in an anodic current on an individual one ofthe electrodes, a total change in cathodic current on the electrodes,and a total change in anodic current on the electrodes.
 24. The methodof claim 15, wherein the difference value is a function of one of anelectrical field, absolute potential, current density, an activatingfunction, and a total net driving function that is derived from theimmediate virtual multipole and the new virtual multipole.
 25. Themethod of claim 15, wherein the difference value is a displacementbetween one pole of the immediate virtual multipole and a correspondingpole of the new virtual multipole.
 26. The method of claim 15, furthercomprising conveying electrical energy to the plurality of electrodes inaccordance with the immediate electrode configuration.
 27. The method ofclaim 15, wherein the immediate and new electrode configurations arerespectively immediate and new fractionalized combinations.